PLURAL - Place-level urban-rural indices for the United States from 1930 to 2018

<strong>PLURAL (Place-level urban-rural indices)</strong> is a framework to create continuous classifications of "rurality" or "urbanness" based on the spatial configuration of populated places. PLURAL makes use of the concept of "remoteness" to characterize the level of spatial isolation of a populated place with respect to its neighbors. There are two implementations of PLURAL, including (a) PLURAL-1, based on distances to the nearest places of user-specified population classes, and (b) PLURAL-2, based on neighborhood characterization derived from spatial networks. PLURAL requires simplistic input data, i.e., the coordinates (x,y) and population p of populated places (villages, towns, cities) in a given point in time. Due to its simplistic input, the PLURAL rural-urban classification scheme can be applied to historical data, as well as to data from data-scarce settings. Using the PLURAL framework, we created place-level rural-urban indices for the conterminous United States from 1930 to 2018. Rural-urban classifications are essential for analyzing geographic, demographic, environmental, and social processes across the rural-urban continuum. Most existing classifications are, however, only available at relatively aggregated spatial scales, such as at the county scale in the United States. The absence of rurality or urbanness measures at high spatial resolution poses significant problems when the process of interest is highly localized, as with the incorporation of rural towns and villages into encroaching metropolitan areas. Moreover, existing rural-urban classifications are often inconsistent over time, or require complex, multi-source input data (e.g., remote sensing observations or road network data), thus, prohibiting the longitudinal analysis of rural-urban dynamics. We developed a set of distance- and spatial-network-based methods for consistently estimating the remoteness and rurality of places at fine spatial resolution, over long periods of time. Based on these methods, we constructed indices of urbanness for 30,000 places in the United States from 1930 to 2018. We call these indices the place-level urban-rural index (PLURAL), enabling long-term, fine-grained analyses of urban and rural change in the United States. The method paper has been peer-reviewed and is published in "Landscape and Urban Planning". The PLURAL indices from 1930 to 2018 are available as CSV files, and as point-based geospatial vector data (.SHP). Moreover, we provide animated GIF files illustrating the spatio-temporal variation of the different variants of the PLURAL indices, illustrating the dynamics of the rural-urban continuum in the United States from 1930 to 2018. <strong>Apply the PLURAL rural-urban classification to your own data: </strong>Python code is fully open source and available at https://github.com/johannesuhl/plural. <strong>Data sources:</strong> Place-level population counts (1980-2010) and place locations 1930 - 2018 were obtained from IPUMS NHGIS, (University of Minnesota, www.nhgis.org; Manson et al. 2022). Place-level population counts 1930-1970 were digitized from historical census records (U.S. Census Bureau 1942, 1964). <strong>References:</strong> Uhl, J.H., Hunter, L.M., Leyk, S., Connor, D.S., Nieves, J.J., Hester, C., Talbot, C. and Gutmann, M., 2023. Place-level urban–rural indices for the United States from 1930 to 2018. <em>Landscape and Urban Planning</em>, <em>236</em>, p.104762. DOI: https://doi.org/10.1016/j.landurbplan.2023.104762 Steven Manson, Jonathan Schroeder, David Van Riper, Tracy Kugler, and Steven Ruggles. IPUMS National Historical Geographic Information System: Version 16.0 [dataset]. Minneapolis, MN: IPUMS. 2021. http://doi.org/10.18128/D050.V16.0 U.S. Census Bureau (1942). U.S. Census of Population: 1940. Vol. I, Number of Inhabitants. U.S. Government Printing Office, Washington, D.C. U.S. Census Bureau (1964). U.S. Census of Population: 1960. Vol. I, Characteristics of the Population. Part I, United States Summary. U.S. Government Printing Office, Washington, D.C.

<strong>点位级城乡指数框架（Place-level urban-rural indices，简称PLURAL）</strong>是一套用于基于居民点（populated places）空间布局构建"乡村性"（rurality）或"城市性"（urbanness）连续分类结果的方法体系。PLURAL借助"偏远性"（remoteness）概念，刻画居民点相对于邻近居民点的空间孤立性（spatial isolation）程度。PLURAL包含两种实现方式：(a) PLURAL-1，基于到用户指定人口等级的最近居民点的距离；(b) PLURAL-2，基于由空间网络（spatial networks）推导得到的邻域特征（neighborhood characterization）。PLURAL所需输入数据极为简洁，仅需特定时点下居民点（村庄、城镇、城市）的坐标(x,y)与人口规模p。由于其输入数据简洁，PLURAL城乡分类体系可应用于历史数据，亦可用于数据匮乏场景。
借助PLURAL框架，我们构建了1930年至2018年美国本土（conterminous United States）的点位级城乡指数。城乡分类对于分析城乡连续体（rural-urban continuum）上的地理、人口、环境与社会过程至关重要。然而，现有多数分类仅能在相对聚合的空间尺度上获取，例如美国的县级尺度。当研究关注的过程具有高度局域性时（如乡村城镇与村庄并入扩张中的都市区），缺乏高空间分辨率的乡村性或城市性测度会带来显著障碍。此外，现有城乡分类往往在时间维度上缺乏一致性，或需要复杂的多源输入数据（如遥感观测或道路网络数据），因此无法开展城乡动态的纵向分析（longitudinal analysis）。
我们开发了一套基于距离与空间网络的方法，能够在长时段内以精细空间分辨率一致估算居民点的偏远性与乡村性。基于这些方法，我们构建了1930年至2018年美国3万个居民点的城市性指数。我们将该指数命名为点位级城乡指数（PLURAL），借此实现美国城乡变化的长期、细粒度分析。本方法相关论文已通过同行评审并发表于《Landscape and Urban Planning》（景观与城市规划）。
1930年至2018年的PLURAL指数可通过CSV文件与基于点的地理空间矢量数据（.SHP）获取。此外，我们还提供了动态GIF文件（animated GIF files），用于展示不同版本PLURAL指数的时空变化（spatio-temporal variation），直观呈现1930年至2018年美国城乡连续体的动态演变过程。
<strong>将PLURAL城乡分类应用于您自有数据：</strong>完整开源（open source）Python代码可在https://github.com/johannesuhl/plural获取。
<strong>数据来源：</strong>1980-2010年点位级人口统计数据与1930-2018年居民点位置数据源自IPUMS NHGIS（明尼苏达大学，www.nhgis.org；Manson et al. 2022）。1930-1970年点位级人口统计数据源自历史普查记录的数字化成果（美国人口普查局1942、1964）。
<strong>参考文献：</strong>Uhl, J.H., Hunter, L.M., Leyk, S., Connor, D.S., Nieves, J.J., Hester, C., Talbot, C. and Gutmann, M., 2023. Place-level urban–rural indices for the United States from 1930 to 2018. <em>Landscape and Urban Planning</em>, <em>236</em>, p.104762. DOI: https://doi.org/10.1016/j.landurbplan.2023.104762
Steven Manson, Jonathan Schroeder, David Van Riper, Tracy Kugler, and Steven Ruggles. IPUMS National Historical Geographic Information System: Version 16.0 [dataset]. Minneapolis, MN: IPUMS. 2021. http://doi.org/10.18128/D050.V16.0
U.S. Census Bureau (1942). U.S. Census of Population: 1940. Vol. I, Number of Inhabitants. U.S. Government Printing Office, Washington, D.C.
U.S. Census Bureau (1964). U.S. Census of Population: 1960. Vol. I, Characteristics of the Population. Part I, United States Summary. U.S. Government Printing Office, Washington, D.C.